Neuromodulation techniques such as transcranial direct current stimulation (tDCS) are routinely used for treating neurological and neuropsychiatric disorders, and for enhancement of cognitive abilities. Recently, their effectiveness in modulating behavioral and neural responses has been questioned. Here we use excitatory and inhibitory tDCS prior to a functional magnetic resonance imaging (fMRI) experiment to show that neural responses for an area's preferred stimuli depend on the polarity of stimulation. This is an important, yet overlooked, data point in demonstrating the effectiveness of these stimulation techniques. Our results show that response preferences in the target area are dependent on the polarity of the tDCS session preceding the fMRI experiment - these preferences are less distinct in the cathodal than in the anodal session. As such, we show unequivocally that tDCS modulates neural responses. This result is of the utmost importance in demonstrating the effectiveness of tDCS for clinical and experimental purposes.

The spatial coordinate system in which a stimulus representation is embedded is known as its reference frame. Every visual representation has a reference frame [1], and the visual system uses a variety of reference frames to efficiently code visual information [e.g., 1, 2, 3-5]. The representation of faces in early stages of visual processing depends on retino-centered reference frames, but little is known about the reference frames that code the high-level representations used to make judgements about faces. Here we focus on a rare and striking disorder of face perception -hemi-prosopometamorphopsia (hemi-PMO) -to investigate these reference frames. Following a left splenium lesion, Patient A.D. perceives features on the right side of faces as if they had melted. The same features were distorted when faces were presented in either visual field, at different in-depth rotations, and at different picture-plane orientations including upside-down. A.D.'s results indicate faces are aligned to a view-and orientation-independent face template encoded in a face-centered reference frame, that these face-centered representations are present in both the left and right hemisphere, and that the representations of the left and right halves of a face are dissociable. KeywordsFace processing; Hemi-Prosopometamorphopsia; View-independent face representation; Splenium; Highlights• After a left splenium lesion, A.D. sees features in right face halves as distorted • A.D.'s distortions affect the same features under all stimulus manipulations tested • Face processing involves a view-and orientation-independent face template • The face vertical midline is an important representational divide in face processing In BriefAfter a left splenium lesion, patient A.D. sees the right halves of faces as melting. Almeida et al.show that the distortion affects the same features regardless of position, rotation in-depth, or in-plane inversion, indicating that faces are encoded in a view-and orientation independent manner.